1. Field of the Invention
This invention relates to a method and apparatus for forming a thin film or a thin film pattern of high accuracy on substrates including a semiconductor substrate.
2. Description of the Prior Art
As is well known in the art, large scale integrated circuits have become more highly integrated with a higher degree of miniaturization of pattern dimension and more advanced three dimentionality of devices. This involves the following various problems. First, it becomes difficult to form a pattern of high accuracy on substrate. This is because when the pattern dimension becomes finer, the pattern density and steps on a substrate give a more conspicuously adverse influence on the dimensional accuracy, with a lowering of the dimensional accuracy. Second, the step reduction or flattening of substrate is difficult to realize. This is because when a pattern is dimensionally miniaturized, steps on substrate becomes sharp. For further integration of large scale integrated circuit, the above difficulties or problems should be solved. These problems are described more particularly.
In prior art, patterning on substrate is usually performed by a procedure which comprises forming a radiation-sensitive organic thin film on a substrate, irradiating the film with a radiation in an imagewise pattern, and contacting the irradiated film with a developer. This is particularly shown in FIG. 1, which schematically shows the step of contacting the thin film with the developer. In the figure, a substrate 1 is contacted with a developer 10 whereupon regions 30 of an organic thin film irradiated with a radiation is dissolved in the developer 10 and removed. On the other hand, regions 31 of the organic thin film which have not been irradiated remain undissolved to obtain a desired pattern. In this procedure, the areal density of the thin film regions 30 irradiated with the radiation differs locally and thus, the concentration of the organic matter dissolved in the developer 10 is also varied locally. The local variation in the concentration of the organic matter in the developer 10 entails a difference in dissolution velocity of the organic thin film at the regions irradiated with the radiation with the dissolution velocity becoming locally irregular. Accordingly, the dimensional accuracy of the resultant pattern is lowered and thus a desired pattern cannot be obtained. Although the dissolution power for the irradiated organic thin film can be rendered uniform when the developer 10 contacting the substrate 1 is efficiently replaced by a fresh one, the developer is usually so viscous that the efficient replacement is not easy. In addition, when the substrate has a deep groove such as a trench, the developer 10 in the groove cannot be exchanged efficiently. The developing velocity for the irradiated organic thin film in the groove lowers with a long time being required for complete removal of the film in the groove. The long-time developing will lower the dimensional accuracy of the pattern. These problems can be solved when the developer in contact with the substrate can be efficiently replaced by a fresh one. More particularly, a solution developer having a low viscosity has to be used in order to solve the problems. In the prior art methods, however, it is essential to use liquids at normal temperatures, thus making it difficult to obtain a solution developer with a small viscosity.
Another problem of the step reduction of flattening of substrate has been conventionally coped with a technique wherein the surface of a dielectric film for layer insulation is flattened. The layer dielectric film used is ordinarily an inorganic thin film. The conventional inorganic thin film is so poor in step coverage with the attendant problem that slips are undesirably formed or even cracks may be formed when the film is made thick. To overcome this, there have been recently developed a chemical vapor deposition method using, for example, tetraethoxysilane, Si(OC.sub.2 H.sub.3).sub.4, and a method using spin-on-glass (SOG) materials containing organic functional groups. This enables one to improve the step coverage and to form a thick film. However, the thin film formed by these methods contains a solvent and organic functional groups therein. When the solvent or organic functional groups are left in the thin film, a problem arises in a procedure subsequent to the formation of the thin film, with lowerings of yield and reliability. This is particularly described with reference to FIG. 2. In FIG. 2, a silicon oxide film is formed as a second layer dielectric film 201 of a semiconductor device of FIG. 2 by a known spin coating technique. If a solvent remains in the second layer dielectric film 201, a leakage current generates between a first aluminum wiring b (202a) and a first aluminum wiring a (202b). Also, a leakage current appears between the first aluminum wiring a and a second aluminum wiring 203. Such a leakage current will cause a final product to be defective with a lowering of yield. Moreover, if the concentration of a remaining solvent in the second dielectric film 201 is high, the first aluminum wirings 202a and 202b and the second aluminum wiring 203 which are in contact with the second layer dielectric film 201 suffer corrosion. The corrosion of the wirings will lower the reliability of the product. In FIG. 2, indicated at 204 is a p-type semiconductor substrate, at 205 is a field oxide film, at 206 is a gate oxide film, at 207 is a gate electrode, at 208 is an n-type diffusion layer, at 209 is a first dielectric film, at 210 is a contact hole and at 211 is a through-hole. The thermal treatment at high temperatures enables one to eliminate organic matters or organic functional groups from the thin film but will produce cracks in the film with a considerable lowering of yield. Accordingly, there has been a demand for a new method of removing the organic matters or organic functional groups from the thin film. Moreover, the known spin-on-glass (SOG) thin film formation method has a difficulty in obtaining a thick film. This is because, in the SOG method, the thermal treatment is used for both removal of solvent and formation of chemical bonds. The removal of solvent brings about shrinkage of the film. This shrinkage will pull SiO.sub.2 bonds being formed and thus cause partial breakage of the bonds, resulting in cracks. For preventing the cracking and achieving formation of a thin film, it is necessary that the chemical bonds be formed subsequent to the removal of solvent.